Method of manufacturing a hollow body by loading such a hollow body blank seated in a cavity with an internal pressure under increased temperature

ABSTRACT

The subject matter of the invention is a method of manufacturing a hollow body ( 1, 10 ) by applying to such a hollow body blank seated in a cavity an internal pressure at increased temperature, wherein said hollow body blank is made using at least one previous forming or master shaping process, said hollow body blank differing by at least 10% in circumferential length on its circumference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application DE 10 2009 010 490.9 filed Feb. 25, 2009.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a hollow body by loading such a hollow body blank, which is seated in a cavity, with an internal pressure under increased temperature.

BACKGROUND OF THE INVENTION

Methods of the type mentioned herein above are well known. So-called internal high-pressure forming methods are known, i.e., methods for hydrostatically forming hollow bodies, the forming occurring substantially at room temperature. Such a method is known from DE 41 03 082 C2 for example.

From the document DE 196 42 824 A1 for example, it is however also known to load a hollow profile body made from metal with an internal pressure with the help of heated oil, wherein it is intended to avoid undesired changes in the structure by subsequent fast cooling of the workpiece.

A method of widening a hollow body by loading it with a pressurized gas at increased temperature is also described in the document DE 10 2004 013 872 B4.

From the document DE 102 20 429.2 B4 there is also known a method of manufacturing a hollow metal body with a cross sectional shape changing in the longitudinal direction in a tool mould configured to conform to the desired final contour. Forming hereby occurs at increased temperatures, the temperature provided in the regions of the highest degrees of deformation being higher than in the regions of lower degrees of deformation. It is also known hereby to compress the hollow body in order to allow for further material to be fed.

From the document DE 199 44 679 C there is known a method wherein a tubular blank is pushed further, meaning is compressed, with internal pressure at its two ends during hot forming. The blank is hottest in the region of the highest degree of deformation.

All these blanks or cavity forms have in common that such a tubular hollow body is open at the two ends of the tube or in the axis of deformation and that it has substantially the same circumferential length distributed over the body or over the surface area of the body.

When forming hollow bodies by means of internal pressure under increased temperature the aim is to obtain substantially the same material thickness or a desired wall thickness gradient through the deformed region, even if these bodies have very different cross sections after forming. In parts, this premise is met if the hollow body blanks have a differing material cross section over their surface area. Additionally, there is the possibility of compressing or also of lengthening such a hollow body in order to ensure substantially the same material thickness or a desired wall thickness gradient over the surface area of the hollow body. It has been found that the measures described herein above do not always suffice to approximate the goal of forming a hollow body having substantially the same or desired material cross section over the surface area.

SUMMARY OF THE INVENTION

To achieve this objective of a hollow body having the same or any material cross section over the surface area, it is proposed, in accordance with the invention, that the hollow body blank differs by at least 10% in circumferential length on its surface. This means that the core of the invention consists in giving the hollow body blank, which is for example made using a forming procedure such as deep drawing or using a forming procedure such as casting, a shape that resembles to a certain extent the final shape of the hollow body. This means that at least in those parts of the hollow body that are experiencing a big change in cross section during internal pressure forming at increased temperature this change in cross section is anticipated to a certain extent by the shape given to the hollow body blank.

Fields of application of hollow bodies are known in which only one end is open, the other end having to be closed though. This is known for example from certain taps or in particular also from doorknobs. Using such a hollow body as a blank, it is always necessary that this tubular hollow body be closed at one end after hot forming. This occurs for example by welding or brazing and always results in a change in structure. If one performs thereafter an anodization for example, the change in structure always remains optically visible, which often is not desirable for aesthetical reasons. Moreover, the method is more expensive due e.g. to the additional welding process. Insofar, it is also known to make such type hollow bodies as a cast design, a welded design or as an assembled design or similar. These methods are however complex and expensive since expensive refinishing is often needed, in particular when the corresponding items are to be anodized thereafter. Insofar, there is provided to configure the hollow body blank so as to be closed at one end or to provide a hollow body blank that comprises only one open end. The bottom may hereby also have an opening that may finally serve to cut a thread for a water outlet for example.

Through a hollow body blank closed at one end, which also preferably only comprises one open end, it is possible to design hollow bodies which substantially need no refinishing, for example by closing the one end by welding, and which, accordingly, are free from structural changes, which remain visible when anodization or chromium plating are performed for example. Such type hollow body blanks with only one open end, which accordingly preferably have a bottom at another end, can for example be manufactured in principle in any shape at low cost by way of extrusion such as by forward and/or backward can extrusion or by deep drawing. For subsequent forming, these blanks are loaded with internal pressure such as by a gas, by deformation bodies (elastically compressible), bulk goods or a liquid in a cavity of a die. There is in particular the possibility to realize different wall thicknesses on deep drawn, forward and backward extruded blanks that are closed by forging or rolling. This means for example that, in the region of higher degrees of deformation, great wall thicknesses are provided in order to achieve a profiled hollow body having substantially the same wall thickness over the length after forming at elevated or increased temperatures. For reasons of strength or of rigidity for example, the objective may however also be to have different wall thicknesses. In this case, it is not absolutely necessary to feed further material in the sense of compressing or drawing the blank in these regions. According to the invention, the hollow body already has a particular shape as it is recited for example in claim 1. This particular shape takes into account the final shape after internal pressure forming under increased temperature, i.e., the shape of the hollow body blank anticipates to a certain extent the final shape. It may still be necessary to compress or to draw the hollow body blank during forming.

It has been found out that, through the previous mechanical forming, such as by deep drawing or extrusion, the material for the consecutive forming process has considerably improved properties over a simple compression moulded tube for example. The reason therefore is in particular that bodies formed under pressure and in particular hot formed bodies have a fine grain; as a result, when the body is then formed under internal pressure, possibly also at increased temperature, there will be no need for re-finishing, e.g., before subsequent anodization or polishing. The reason therefore is that the body has substantially no or only few rough spots, which is due to the fine-grain structure and the material consolidation of the blank. The hollow body blanks in particular, which are hot formed with a closed end, have no weld seams or burrs affecting further internal pressure forming due to the different structures. It has also been found out that blanks made by master shaping such as casting also exhibit material properties that experience no or only slight changes in the structure during the subsequent forming procedures by means of internal pressure and increased temperature.

There may be further provided that the hollow body is compressed at the closed end. As already explained herein above, the compression of the workpiece serves to feed material, in particular to achieve uniform wall thickness or the required wall thickness profile over the deformation axis or the surface area of the workpiece. There may be further provided that the hollow body is additionally deformed in the region of the closed end during compression.

Further advantageous features and designs are recited in the dependent claims.

According to an embodiment, there is provided that the hollow body blank is configured to be spherical, by way of forming or master shaping, the blank having at least one opening. Such a body may also have a circumferential length that differs by at least 10% on its surface.

There is in particular provided that the hollow body has a higher temperature in the region of higher degrees of deformation or of greater wall thicknesses than in the region of lower degrees of deformation or of thinner walls. Another advantage is obtained if the forming temperature is lower than the melting temperature of the material of the workpiece. To prevent scaling of corrosion prone materials such as copper, steel titanium and so on or to prevent the risk of burning when oxygen is fed (magnesium, titanium, steel), one uses an inert gas such as nitrogen or argon for applying the internal pressure; otherwise, air is being used.

As already explained herein above, hollow bodies that are to be at elevated or increased temperatures formed may show great differences in the degrees of deformation, which is finally made possible by a temperature profile provided to correspond to the desired degrees of deformation.

It may be further provided to heat the hollow body partially or completely before placing it into the cavity, in particular to heat it with a temperature profile that correlates with the desired degrees of deformation or with the course of deformation via the axis of deformation of the hollow body. Moreover, the cavity may also be additionally heated completely or partially, in particular according to the temperature profile of the hollow body or as a complement to the hollow body. More specifically, there is advantageously provided in this context that the hollow body has a heat profile with temperature differences ranging for example between 2° and 100° C. in order for deformation to be carried out in the desired deformation sequence. Longer hollow bodies are easier to form with greater temperature differences than short hollow bodies. This means that, thanks to the temperature profile, it is achieved that deformation is induced at a certain place, namely in most cases at the places having the highest degrees of deformation or wall thicknesses in order for example to ensure in particular that forming occurs securely with the least possible friction at the wall of the cavity.

According to another feature of the invention, the hollow body is tempered after internal pressure forming, using the forming heat. This means that the hollow body is cooled down from the forming heat according to the desired structure properties.

Further, the hollow body may be bent before internal pressure forming, at need at increased temperature, which means that the bending process occurs before the forming process used for manufacturing the blank, which is to be hot formed. This however also means that the blank has been deep drawn for example before bending. Further, the hollow body can be formed by the die when said forming die is being closed; an oval cross section may for example be made from a round cross section.

It may also be envisaged that the hollow body consists of several parts, which communicate together for the forming medium to pass through, or which can establish a communication through internal pressure, such as by causing the partitioning wall to burst. It may also be envisaged that the connection may be kept closed. It is obvious there from that a hollow body may for example be formed, which has only one opening in the axis of deformation but which has for example a branch that is connected to the hollow body for forming pressure to build up.

It may also be envisaged that the hollow body blank projects from the cavity. When the hollow body blank is compressed or drawn, sealing occurs when internal pressure is applied in the region of the device for applying pushing or pressure forces by means of which the blank is compressed or drawn. This means that the blank is sealed outside of the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in closer detail herein after with reference to the drawings.

FIG. 1 a shows a deep drawn blank with an inner diameter that differs over the length, the one end of the blank being closed;

FIG. 1 b shows for example a shape after hot forming under internal pressure of the body as shown in FIG. 1 a under internal pressure and increased temperature;

FIG. 2 a shows a body as a blank as shown in FIG. 1 a, but with no circular outlet cross sections;

FIG. 2 b shows a hollow body as an end product with examples of different cross sectional shapes through the axis of deformation of the hollow body;

FIG. 3 a, 3 b show blanks which have another outer contour before internal pressure forming at elevated temperatures;

FIG. 4 shows a configuration of a blank for hot forming as shown in FIG. 2 b, only the closed front side end having a conical contour;

FIG. 5 shows an illustration of a blank as shown in FIG. 4 with a half spherical front side contour;

FIG. 5 a shows a blank as shown in FIG. 5 with a varying wall thickness gradient on the circumference;

FIG. 6 shows an embodiment wherein the blank has an attached piece before forming at elevated temperatures;

FIG. 7 a, 7 b show other examples of hollow body blanks;

FIG. 8-8 b show examples of spherical hollow body blanks;

FIG. 9 shows a configuration as shown in FIG. 1, with the bottom only having one opening.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The blank shown in FIG. 1 a is indicated at 1. The blank 1 has a wall thickness that varies over its length (arrow 2). The one front side end (arrow 3) of the blank 1 is closed. After forming of the blank according to FIG. 1 a, the hollow body is like shown in FIG. 1 b for example. The wall thickness is hereby completely different, this being also due to the fact that the hollow body has not been substantially compressed in the thickened regions for feeding further material during forming at elevated temperatures.

The illustration shown in the FIGS. 2 a and 2 b substantially differs from the FIGS. 1 a and 1 b by the fact that the hollow body blank shown in FIG. 2 b may possess three different cross sectional shapes 5, 6 and 7, namely oval, round and rectangular. The shape of the blank thus corresponds to the shape of the cavity in which the blank is formed when subject to internal pressure.

FIG. 3 a shows an initial shape of a blank 1 having a constricted end before internal pressure forming. FIG. 3 b shows an initial shape of a blank 1 with a constricted and widened end before internal pressure forming.

The FIGS. 4 and 5 show the hollow body blank 1 with a different front face (arrows 8 and 9).

FIG. 5 a shows a hollow body as a blank having a varying wall thickness gradient over the circumference. Through the varying wall thickness, it is taken into account that, e.g., in case of different degrees of deformation, approximately the same wall thickness is to be achieved over the circumference of the hollow body or that the desired wall thickness distributions are achieved.

In the illustration of the hollow body blank shown in FIG. 6, the hollow body 1 comprises an attached piece 20 that is connected to the hollow body by welding, brazing or e.g., by clinching. If the attached piece is to be deformed also, the transition to the hollow body 1 (arrow 12) may be open. However, it is also possible that the connection to the attached piece 20 is at first closed by a partitioning wall 12, which however bursts when subject to an appropriate internal pressure, so that then the attached piece is also formed accordingly under internal pressure at increased temperature. The wall in the transition to the attached piece 20 may however also be configured so as to be preserved during internal pressure forming.

The FIGS. 7 a and 7 b show examples for hollow body blanks that have substantially the same diameter and width or that have different circumferential lengths on their circumferential inner and outer surface area.

The FIGS. 8 through 8 b show spherical hollow body blanks 10 having an attached piece 10 a for injecting a forming medium e.g. gas, for generating the internal pressure with an additional opening 10 b (FIG. 8 a). FIG. 8 b shows a spherical hollow body 10 with an attached piece 10 a and with an outlet 10 b that is also configured to be a flange-shaped attached piece like in 10 a.

FIG. 9 shows a hollow body blank 1 as shown in FIG. 1, the bottom 3 of which comprises an opening 3 a. 

1. A method of manufacturing a hollow body by applying to such a hollow body blank seated in a cavity an internal pressure at increased temperature, wherein said hollow body blank is made using at least one previous forming or master shaping process, said hollow body blank differing by at least 10% in circumferential length on its circumference.
 2. The method as set forth in claim 1, characterized in that the hollow body blank has only one open end.
 3. The method as set forth in claim 1, characterized in that the hollow body blank comprises a bottom.
 4. The method as set forth in claim 1, characterized in that the bottom comprises an opening.
 5. The method as set forth in claim 1, characterized in that, during internal pressure forming at increased temperatures, the hollow body blank is compressed axially in order to prevent undesired reduction of the wall thickness or in order to increase the wall thickness.
 6. The method as set forth in claim 1, characterized in that, during internal pressure forming at increased temperatures, the hollow body blank is drawn in order to achieve the desired wall thickness distribution.
 7. The method as set forth in claim 1, characterized in that the hollow body is bent before forming or while the cavity is being closed.
 8. The method as set forth in claim 5, characterized in that the hollow body blank is compressed at the closed end.
 9. The method as set forth in claim 8, characterized in that the hollow body blank is additionally deformed in the region of the closed end during compression.
 10. The method as set forth in claim 1, characterized in that the hollow body blank is configured to be spherical and is made by at least one previous forming or master shaping process, said blank comprising at least one opening.
 11. The method as set forth in claim 1, characterized in that the hollow body blank has a higher temperature in regions of higher degrees of deformation and/or wall thicknesses than in regions of lower degrees of deformation and/or wall thicknesses.
 12. The method as set forth in claim 1, characterized in that the temperature for internal pressure forming is lower than the melting temperature of the material of the workpiece.
 13. The method as set forth in claim 1, characterized in that air or an inert gas such as nitrogen or argon is used for applying the internal pressure.
 14. The method as set forth in claim 1, characterized in that the hollow body blank is heated partially or completely.
 15. The method as set forth in claim 1, characterized in that the cavity is heated partially or completely.
 16. The method as set forth in claim 1, characterized in that the hollow body blank and/or the cavity (die engraving) comprises a heat profile with temperature differences preferably ranging between 2° and 100° C. in order to allow for deformation to proceed in the desired deformation sequence.
 17. The method as set forth in claim 1, characterized in that the hollow body blank is tempered from the forming heat after forming.
 18. The method as set forth in claim 1, characterized in that the hollow body blank consists of several parts that communicate with each other for the forming medium to pass through.
 19. The method as set forth in claim 1, characterized in that the hollow body blank is sealed outside the cavity during compression or drawing. 